The present invention relates to a lowering sinker actuation cam set for circular knitting machines for stocking or hosiery-making particularly for forming standard-terry knitting and sandwich-terry knitting.
It is known that knitting with terry stitches is produced in circular knitting machines for stocking or hosiery-making by using specially-provided lowering sinkers provided with two lowering planes, i.e., the planes on which the yarns rest during the descent of the needles of the needle cylinder so as to form loops of knitting, arranged at two mutually different elevations and by dispensing, at one feed of the machine, two yarns which are taken up simultaneously by the needles. The two yarns are dispensed with a particular arrangement of the corresponding yarn guides and the lowering sinkers are actuated so that during the descent of the needles the two yarns are arranged respectively on the lower lowering plane and on the upper lowering plane of the sinkers, forming, for each needle, two loops of different length in which the longer loop provides the characteristic terry effect.
As an alternative to the use of lowering cams with two lowering planes, pairs of lowering sinkers or two side-by-side sinkers are also used which are accommodated in a same radial slot of the sinker ring, each being provided with a lowering plane which is located at a different vertical level than the lowering plane of the other sinker of the same pair. In practice, a pair of these sinkers corresponds to a sinker with two lowering planes located at two mutually different elevations.
In this case it is also possible to actuate only the sinkers with the lower lowering plane to form normal knitting.
Generally, in the manufacture of hosiery items the longer loops which produce the terry effect protrude on the back of the item, whilst the shorter loops are more visible on the right side. The shorter loops are generally formed by using a very thin yarn, usually made of helanca or other similar material, whilst the longer loops, i.e., the loops of terry, are formed with a cotton yarn.
As a consequence of this fact, with conventional terry-stitch knitting, referenced hereinafter as "standard terry" for the sake of clarity, when patterns are formed on the item said patterns have a poor definition, owing to the fact that the shorter loops of standard terry are visible on the right side of the item between the loops of the pattern.
In order to solve this problem, a particular kind of terry-stitch knitting has been devised which is known as "sandwich terry"; in this terry, during the forming of the double loops, the yarn that forms the shorter loops is shifted and kept toward the back of the item, so as to interfere as little as possible with the loops of the pattern and thus allow to achieve better definition of the pattern on the right side of the item.
This effect is achieved mainly by virtue of a particular actuation of the lowering sinkers in order to achieve, after resting the yarn on the lower lowering plane, a movement of the sinkers, or of the sinkers that have said lower lowering plane, away from the axis of the needle cylinder which correspondingly moves the yarn of the shorter loops toward the open side of the tip of the needles, i.e., on the back of the item, differently from ordinary terry knitting, in which the yarn of the shorter loops is shifted in the opposite direction.
The movement of the sinkers away from the axis of the needle cylinder is achieved by virtue of a suitable configuration of the path which is traced by the cams and countercams and in which the heels of the lowering sinkers engage and by using special sinkers.
As an alternative to this solution, special sinkers are also used instead of the sinkers used for standard terry knitting.
In any case, in order to switch from standard-terry knitting to sandwich-terry knitting, with conventional knitting or hosiery-making machine it is necessary to discontinue production and replace the cams that actuate the sinkers and replace the sinkers that engage said cams or at least the sinkers.
For this reason, with currently commercially available machines it is not possible to produce items which are knitted partly with standard-terry knitting and partly with sandwich-terry knitting.
This possibility, which has so far not been allowed, would instead be appreciated, since items manufactured exclusively with standard-terry stitches lead to an unsatisfactory aesthetic result in regions with patterns, whilst items formed exclusively with sandwich-terry knitting provide a better aesthetic result but are not as resistant as standard-terry items.